40 PREDICTORS OF CLONED CALF VIABILITY

Abstract

The high rate of gestational loss in nuclear transfer (NT) pregnancies is a major economic and animal cost, preventing the widespread use of the technique. It is currently not possible to predict which early gestation fetuses will remain viable to term. As placental abnormalties are commonly associated with nonviable fetuses, placental proteins such as pregnancy specific protein (PSP 60, Heyman et al., 2002 Biol. Reprod. 63, 1787–1794; or PSPb Hill et al., 2000 Biol. Reprod. 66, 6–13) have been investigated as possible markers of viable pregnancy. To build upon these studies, we explored the predictive value of Day-35 maternal serum PSPb value to final cloned-calf viability; PSPb profiles throughout pregnancy; and the relationship of maternal plasma estradiol levels to calf viability. Maternal serum was sampled for PSPb at the time of the first ultrasound pregnancy examination (Day 35) to determine fetal number and viability (heartbeat). PSPb values were determined using an RIA by Dr. Garth Sasser (BioTracking, Moscow, ID). Median PSPb values were compared using the Kruskal-Wallis one-way ANOVA test on ranks. PSPb levels from failed single and twin pregnancies were significantly different from those of AI bred controls (P < 0.05). PSPb levels from failed singles were not significantly different from those of viable single pregnancies although only nonviable cloned pregnancies had PSPb values >7.5. As PSPb levels at Day 35 were not highly predictive of viable outcome, we detailed the gestational PSPb profile for a different group of cows (n = 40) that carried cloned pregnancies beyond Day 90. PSPb was determined at Days 35, 50, 65, and 90, then monthly to Day 240. Although there was no clear statistical significance, PSPb levels from nonviable cloned pregnancies were consistently higher at each time point than for viable pregnancies (14 cows gave birth to live calves) and significantly higher than those of controls. At term, plasma estradiol concentrations were assessed in a group of 5 NT pregnancies. Estradiol was investigated as cloned pregnancies often show a lack of readiness for parturition (e.g. lack of udder development, prolonged gestation, dysmature calves). These 5 pregnancies produced 3 highly viable NT calves: 1 with lowered viability that survived only with a high level of intensive care, and 2 nonviable despite a high level of assistance. In this small group, estradiol levels on the day of birth rose in parallel with viability (viable, 662 pg; lowered viability, 170 pg; nonviable, 76 pg). This is a clinical observation rather than a statistical trend that suggests further investigation may be warranted. In summary, our results suggest maternal PSPb levels have value in identifying the outliers in a population of cloned pregnancies and that term-cloned pregnancies may show abnormally low maternal estradiol concentrations at term.

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